chore: abstract plain text settings into a SpannerOption (#4264)

* chore: abstract plain text settings into a SpannerOption

* add unit test for plain text scenarios

* gemini suggested code changes

* updated javadoc

* missing space

* fixed unit test

---------

Co-authored-by: rahul2393 <irahul@google.com>

Author: sagnghos

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java

@@ -914,7 +914,7 @@ protected SpannerOptions(Builder builder) {
     openTelemetry = builder.openTelemetry;
     enableApiTracing = builder.enableApiTracing;
     enableExtendedTracing = builder.enableExtendedTracing;
-    if (builder.isExperimentalHost) {
+    if (builder.experimentalHost != null) {
       enableBuiltInMetrics = false;
     } else {
       enableBuiltInMetrics = builder.enableBuiltInMetrics;
@@ -1139,7 +1139,8 @@ public static class Builder
     private boolean enableBuiltInMetrics = SpannerOptions.environment.isEnableBuiltInMetrics();
     private String monitoringHost = SpannerOptions.environment.getMonitoringHost();
     private SslContext mTLSContext = null;
-    private boolean isExperimentalHost = false;
+    private String experimentalHost = null;
+    private boolean usePlainText = false;
     private TransactionOptions defaultTransactionOptions = TransactionOptions.getDefaultInstance();
 
     private static String createCustomClientLibToken(String token) {
@@ -1675,10 +1676,18 @@ public Builder setHost(String host) {
 
     @ExperimentalApi("https://github.com/googleapis/java-spanner/pull/3676")
     public Builder setExperimentalHost(String host) {
+      if (this.usePlainText) {
+        Preconditions.checkArgument(
+            !host.startsWith("https:"),
+            "Please remove the 'https:' protocol prefix from the host string when using plain text communication");
+        if (!host.startsWith("http")) {
+          host = "http://" + host;
+        }
+      }
       super.setHost(host);
       super.setProjectId(EXPERIMENTAL_HOST_PROJECT_ID);
       setSessionPoolOption(SessionPoolOptions.newBuilder().setExperimentalHost().build());
-      this.isExperimentalHost = true;
+      this.experimentalHost = host;
       return this;
     }
 
@@ -1789,6 +1798,23 @@ public Builder useClientCert(String clientCertificate, String clientCertificateK
       return this;
     }
 
+    /**
+     * {@code usePlainText} will configure the transport to use plaintext (no TLS) and will set
+     * credentials to {@link com.google.cloud.NoCredentials} to avoid sending authentication over an
+     * unsecured channel.
+     */
+    @ExperimentalApi("https://github.com/googleapis/java-spanner/pull/4264")
+    public Builder usePlainText() {
+      this.usePlainText = true;
+      this.setChannelConfigurator(ManagedChannelBuilder::usePlaintext)
+          .setCredentials(NoCredentials.getInstance());
+      if (this.experimentalHost != null) {
+        // Re-apply host settings to ensure http:// is prepended.
+        setExperimentalHost(this.experimentalHost);
+      }
+      return this;
+    }
+
     /**
      * Sets OpenTelemetry object to be used for Spanner Metrics and Traces. GlobalOpenTelemetry will
      * be used as fallback if this options is not set.
@@ -1954,7 +1980,7 @@ public Builder setDefaultTransactionOptions(
     @Override
     public SpannerOptions build() {
       // Set the host of emulator has been set.
-      if (emulatorHost != null) {
+      if (emulatorHost != null && experimentalHost == null) {
         if (!emulatorHost.startsWith("http")) {
           emulatorHost = "http://" + emulatorHost;
         }
@@ -1964,7 +1990,7 @@ public SpannerOptions build() {
         this.setChannelConfigurator(ManagedChannelBuilder::usePlaintext);
         // As we are using plain text, we should never send any credentials.
         this.setCredentials(NoCredentials.getInstance());
-      } else if (isExperimentalHost && credentials == null) {
+      } else if (experimentalHost != null && credentials == null) {
         credentials = environment.getDefaultExperimentalHostCredentials();
       }
       if (this.numChannels == null) {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/testing/ExperimentalHostHelper.java

@@ -16,10 +16,8 @@
 
 package com.google.cloud.spanner.testing;
 
-import com.google.cloud.NoCredentials;
 import com.google.cloud.spanner.SpannerOptions;
 import com.google.common.base.Strings;
-import io.grpc.ManagedChannelBuilder;
 
 public class ExperimentalHostHelper {
   private static final String EXPERIMENTAL_HOST = "spanner.experimental_host";
@@ -58,9 +56,7 @@ public static void setExperimentalHostSpannerOptions(SpannerOptions.Builder buil
     builder.setExperimentalHost(experimentalHost);
     builder.setBuiltInMetricsEnabled(false);
     if (usePlainText) {
-      builder
-          .setChannelConfigurator(ManagedChannelBuilder::usePlaintext)
-          .setCredentials(NoCredentials.getInstance());
+      builder.usePlainText();
     }
     if (isMtlsSetup()) {
       String clientCertificate = System.getProperty(CLIENT_CERT_PATH, "");

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SpannerOptionsTest.java

@@ -1360,4 +1360,27 @@ public void testCreateDefaultDynamicChannelPoolOptions() {
     assertEquals(
         SpannerOptions.DEFAULT_DYNAMIC_POOL_CLEANUP_INTERVAL, defaults.getCleanupInterval());
   }
+
+  @Test
+  public void testPlainTextOptions() {
+    SpannerOptions options =
+        SpannerOptions.newBuilder().setExperimentalHost("localhost:8080").usePlainText().build();
+    assertEquals("http://localhost:8080", options.getHost());
+    assertEquals(NoCredentials.getInstance(), options.getCredentials());
+    options =
+        SpannerOptions.newBuilder()
+            .setExperimentalHost("http://localhost:8080")
+            .usePlainText()
+            .build();
+    assertEquals("http://localhost:8080", options.getHost());
+    options =
+        SpannerOptions.newBuilder().usePlainText().setExperimentalHost("localhost:8080").build();
+    assertEquals("http://localhost:8080", options.getHost());
+    options =
+        SpannerOptions.newBuilder()
+            .usePlainText()
+            .setExperimentalHost("http://localhost:8080")
+            .build();
+    assertEquals("http://localhost:8080", options.getHost());
+  }
 }